The general objective under this grant is the isolation and characterization in brain of enzymes that are related to the special metabolism of that organ. An exoribonuclease from bovine white matter has been purified 1000-fold; current experiments are designed to learn whether the enzyme can be more conveniently prepared on a larger scale from spinal cord, which is a more convenient starting material for bulk extractions than a tissue that needs to be further dissected. The initially insoluble enzyme from white matter that hydrolyzes 2', 3'- cyclic nucleotides has been solubilized and purified 200-fold; the preparation of the enzyme from cord in sufficient quantity for chemical characterization will also be undertaken. Experiments are underway to find phosphate esters which might be more probable naturally ocurring substrates for this enzyme than 2', 3'-cyclic nucleotides. The techniques used for solubilizing this membrane-bound enzyme may be applied to other insoluble proteins in brain. The chromatography of esters of amino acids and peptides of neurochemical concern is being studied on an amino acid analyzer. A 70- minute analysis is being used to measure the half-life in the blood in vitro of L-aspartyl-L-phenylalanine methyl ester, which has recently been introduced by R. H. Mazur and associates as a possible sugar substitute.